1. Field of the Invention
This invention relates to fluorescent lamps and, in particular, to the attachment of power circuitry to such lamps.
2. Description of Related Art
It is well known in the art to electrically connect fluorescent lamps to primary power sources via a variety of different types of power circuitry. For example, complex ballast circuits are commonly provided to perform a number of power-related functions including, inter alia, the conversion of power from the primary sources to AC voltages and frequencies corresponding to the requirements of respective lamps and the limiting and control of the flow of electrical current to the lamps. In recent years, electronic ballasts have been invented which are substantially smaller than their magnetic ballast precursors while even having the capabilities of performing additional functions, e.g. dimming. If the operating frequency is increased, the size of magnetic and filter components of an electronic ballast can be further decreased. As a consequence of increasing the frequency, however, electrical losses tend to increase, particularly because of losses in the impedances of long leads typically used to connect ballasts to lamps. More specifically, the leads have inductive impedances with voltage drops that increase with frequency and parasitic capacitances which bypass current intended for the lamp.
Traditionally, power circuits for fluorescent lamps are incorporated in fixtures for the lamps. This is done primarily because of size, weight, cost and safety factors of such circuits and, especially, in relationship to complex and relatively-heavy ballast circuits. However, if the power circuits can be operationally and cost effectively incorporated in the lamps, rather than in the fixtures, there are many advantages. To name a few:
Each fixture will no longer be limited to use with specific lamp types which are associated with a specific power circuitry installed in the fixture.
It will be impossible for the user to install the wrong lamp in the fixture.
The power circuit and lamp can be optimized to work together to maximize efficiency and lamp life, while minimizing circuit volume and parts count.
Fixtures can be less expensive, more attractive, and have more efficient reflector designs, because they will no longer need to be designed around the power circuitry.
The need for long connection leads will be eliminated, thereby enabling an increase in operating frequency without the consequent increases in electrical losses.
High-voltage power circuitry can be contained within the lamp envelope, thereby reducing shock hazards.
While the prior art, e.g. U.S. Pat. No. 5,485,057, describes miniaturized power circuitry for fitting within the envelope of a lamp, further development is needed to achieve effective containment of the circuitry within the envelope. Such circuitry should be compact while still allowing for effective heat dissipation and facilitating electrical connections to a primary power source and to the lamp itself.
It is an object of the invention to provide a compact structure for supporting power circuitry within a lamp envelope.
It is another object of the invention to provide such a structure which readily adapts to design changes in the power circuitry affecting the number and/or sizes of the circuit components.
It is yet another object of the invention to provide such a structure which facilitates the making of electrical connections to the circuit components and to terminals and electrodes of the lamp itself.
In accordance with the invention a circuit assembly for containment within a longitudinally-extending tubular envelope portion of a fluorescent lamp is provided which includes first and second spaced-apart circuit boards arranged along the longitudinal direction of the envelope portion. Each of the first and second circuit boards has a side extending transversely of the longitudinal direction for supporting at least one circuit component and has a periphery shaped and dimensioned to substantially conform with a circumferential inner surface of the tubular envelope portion. A plurality of longitudinally-extending support members are coupled to the first and second circuit boards for positioning the circuit boards relative to each other. In a preferred form of the invention, the support members comprise electrical conductors which are used for both holding the boards in position and providing electrical connections between the boards.
The size of the circuit assembly is determined by the cross-sectional area of the envelope and by the total area needed to mount circuit components. There need be no wasted space. The circuit assembly is readily adaptable to changes in circuit components by merely increasing or decreasing the number of circuit boards and/or the spacing between the circuit boards.
Further, no additional parts need be provided for supporting the circuit assembly within the envelope. The circuit boards and the conductors perform both structural and electrical functions.